Justification:Gnathonemus longibarbis occurs in the Lake Victoria basin, the Akagera system, the Malagarazi River and the Lake Tanganyika basin. No major, widespread threats have been identified, although this species has suffered local declines in the Lake Victoria basin. This stonebasher is therefore listed as Least Concern.

This species is known from the Lake Victoria basin in Kenya (Seegers et al. 2003) and Uganda (Greenwood 1966), and from the affluent rivers Akagera, Sondu (Corbet 1961) and Nzoia (Balirwa 1979). Gnathonemus longibarbis has also been recorded in the Victoria Nile between Lake Kyoga and the Murchinson Falls (Boulenger 1916), in Lake Kyoga and smaller associated lakes (Worthington 1929) and in Lake Nabugabo (Greenwood 1966). It is found in the Akagera River system in Rwanda (De Vos et al. 2001), in the Malagarazi River basin in Tanzania (Eccles 1992) and Burundi (Banyankimbona et al. 2012), and in the Lake Tanganyika basin (Poll 1946).

It is common in fisheries catches in the Middle Akagera system. It has a large extent of occurrence but is rarely encountered. In Lake Victoria it is nowhere considered common (Greenwood 1966) and in Lake Kyoga it is abundant among or near water lilies (Worthington 1929). Gnathonemus longibarbis disappeared from the open waters of Lake Nabugabo after the introduction of Nile Perch. Over-fishing of the Nile Perch allowed resurgence of this mormyrid, which may have survived in small pockets within the main lake (Chapman and Hulen 2001, Chapman et al. 2003).

In Lake Kyoga, G. longibarbis occurs in or near water lilies and in the Lake Victoria basinit occurs in shallow, inshore waters over sandy and rocky habitats, seasonally over muddy bottoms adjacent to extensive papyrus swamps and also in deep water near rocky islands (Okedi 1971). The depth range is 27–45 m (Okedi 1971). It is insectivorous and feeds on the bottom and in marginal vegetation. Chironomid larvae, Povilla, and Odonata larvae are mainly eaten, but arthropods, oligochaetes and fish eggs are also part of the diet (Corbet 1961). Gnathonemus longibarbis uses its sensitive pointed addition to its chin for testing holes in mud, papyrus roots and between stones to locate underwater insects (Copley 1958). It rotates its body to almost vertical position, searches the substrate and grabs its prey into mouth (Nyingi 2013). Okedi (1971) suggested that this mormyrid may withstand low oxygen tensions on a periodic basis because of its benthic feeding activities during which it may probe in deoxygenated mud. It also produces weak electric organ discharge for navigation and to warn off other organisms (Nyingi 2013). This stonebasher breeds twice a year, during the rainy seasons (Okedi 1969), and migrates up rivers to spawn (Whitehead 1959, Okedi 1969). The maximum size is 36.0 cm TL (Seegers et al. 2003).

No threats are known for this species specifically. Water turbidity and siltation as a consequence of erosion and farming expansion, regression of wetlands and swamps due to extension of agriculture and human settlements, irrigation, eutrophication, loss of riverine migratory routes are potential threats. In the Malagarazi River basin, sedimentation and increased use of agrochemicals (pesticides and fertilisers), and pollution from future mining activities (nickel, gold) might threaten this species (West 2001).